The Adamantine Sealing Chains is a fūinjutsu used by members of the Uzumaki clan.
This technique moulds the user's chakra into extremely durable chains which can be used for various purposes, such as directly combating or physically restraining their targets — foes even as powerful as a tailed beast. According to Orochimaru, these chains could also be used to bind the chakra of a target, completely neutralising them. Using her chains, Kushina could also erect a barrier strong enough to prevent anyone or anything from entering or leaving the perimeter defined by the chains. The barrier was very durable, as Hiruzen Sarutobi stated that there was nothing anyone could do to interfere with what Minato and Kushina were doing once it had been erected.
These chains also made up her seal, completely pinning the fox down with several spikes in her own mind. Even while near death, Kushina was able to use these chains in the physical realm to restrain Kurama, enabling Minato Namikaze to use the Dead Demon Consuming Seal.
After Minato sealed a portion of Kushina's chakra inside of Naruto Uzumaki, she was able to manifest a weaker version of this technique through Naruto, which, in conjunction with her "special chakra", Kushina was able to temporarily restrain Kurama in Naruto's subconscious.